1. Field
Example embodiments relate to methods of forming phase-change memory units, methods of manufacturing phase-change memory devices using the same and phase-change memory devices manufactured using the same. More particularly, example embodiments relate to phase-change memory units having an improved electrode structure, methods of manufacturing phase-change memory devices using the same and phase-change memory devices manufactured using the same.
2. Description of the Related Art
Generally, data is stored in a cell of a phase-change memory (PRAM) device using a resistance difference between an amorphous state and a crystalline state of a phase-change material layer including a chalcogenide material. That is, data “0” or “1” are stored in the cell of the PRAM device using a reversible phase change of the phase-change material layer including the chalcogenide material, which may occur according to the amplitude and wavelength of a pulse applied to the phase-change material layer. For example, a reset current needed to change the phase-change material layer from a crystalline state into an amorphous state and a set current needed to change the phase-change material layer from the amorphous state into the crystalline state may flow from a transistor or a diode through a lower electrode to the phase-change material layer, thereby changing the phase of the phase-change material layer.
A phase change of the phase-change material layer may be due to Joule's heat, which is generated as reset/set currents flow through a lower electrode. In order to effectively transfer heat generated using low reset/set currents, it may be desirable to attempt to prevent heat from diffusing into other regions excluding the phase-change material layer, and a contact area between the phase-change material layer and the electrode may be decreased.
Various lower electrode structures have been developed. For example, a structure including a cylindrical conductive contact as a heat generator may be provided on the lower electrode. However, the cylindrical conductive contact is formed by an etching process so that the cylindrical conductive contact may not have a desirable area due to resolution limits of a photolithography process used to form the contact.
The phase-change material layer formed on the cylindrical contact may be patterned by an etching process, such as a photolithography process, and thus the phase-change material layer may be deteriorated by damage generated during the etching process.